The present invention relates, in general, to photon detection and imaging and in one embodiment, specifically, to event sensitive photon detection in an imaging process and detection of photons produced through interactions between an incident beam and material in the object to be imaged.
Computed tomography (CT) is widely used in medical diagnosis. In a typical CT process, a radiation source emits a thin X-ray beam while rotating around a patient. X-ray image detectors positioned at the opposite side of the patient from the radiation source pick up and record data regarding absorption of the X-ray beam by various tissues and bones in the patient. A computer processes the data and generates images that assimilate multiple X-ray images into a two-dimensional cross sectional image. The CT images reveal many soft tissue structures not shown by conventional radiography. In addition, a CT image shows an entire slice of the patient's body with greater clarity compared with a conventional X-ray radiography image using the same dosage of radiation.
A conventional CT is deficient in providing detailed information regarding a small abnormal tissue, e.g., a tumor, in the patient's body. In addition, the intrinsic noise in the electronic circuits may adversely affect the image quality of a conventional CT. Increasing the intensity of the X-ray radiation may improve the signal to noise ratio of the circuits, but will also increase radiation exposure of the patient. Excessive increase in the radiation intensity may also adversely affect the resolution of the images.
Positron emission tomography (PET) detects photons generated through positron-electron annihilation of positrons from a radioactive tracer placed in the object, e.g., patient, to be imaged, and analyzes the photon energy and trajectory to generate tomographic images of the patient. Single photon emission computed tomography (SPECT) generates images by computer analysis of photon emission events from a radioactive tracer. Positron-electron annihilation may be the source of such photon emission. PET and SPECT require the detection and analysis of single photon events. Photomultipliers are generally used for single photon event detection in PET and SPECT. The low spatial resolution of the photomultipliers may adversely affect the quality of PET and SPECT images. Other constraints on the PET and SPECT image qualities include the temporal and spatial resolution and counting rate characteristics of the photomultipliers and associated circuitry.
Accordingly, it would be advantageous to have an apparatus and a method for accurately detecting photon emission events. It is also desirable to have a photon detection apparatus that has a high signal to noise ratio for generating high quality data. It is further desirable to be able to detect the photon emissions with both high spatial resolution and high temporal resolution. It would be of further advantage to be able to produce the PET and SPECT without a radioactive tracer.